Spring Starts?: A 70F Day, Forsythia Blooms, What is GDD? and Seedhead Suppression
This was an “interesting” week. We experienced a pulse of warm temperature mid-week only to slide back down. But on the whole Mother Nature is waking up. Just look around in the landscape and you will see the first colors of spring. YELLOW. Yes, many of the earliest flowers that we see are often yellow. Some can be used to help growers (and superintendents) time inputs better than the calendar. It’s called phenology. Simply put it is “the study of periodic events in biological life cycles.” Examples are many, but growers (us) like to use the date and emergence of leaves and flowers. Every year is different and so far 2022 is a slow, wet spring. But wait, a 70 degree day this week! April 13 felt good. Overall, the last 7 days were not so good. With quick cadence, severe thunderstorms moved across the Midwest. Saturated. A return to predominately cool, wet, WINDY conditions = a damper on it feeling like spring. But we did experience a little bit of warmth this week. Come back.
Weather Summary (April week 2) by Shehbaz Singh, MS
Air Temperature. Finally, Chicago has seen its first day of air temperature above 70° F. That meant temperatures were higher than the normal range. Highest temperature of 72° F was recorded on April 13th and interestingly the lowest temperature of 39° F was also recorded on the very same day. Normally, air temperature for this week in April ranges from 40 to 58° F. Last year, the air temperatures at this point in April were lower.
Precipitation. So far in April, Chicago has received about 2.05 inches of precipitation. This is higher than the normal precipitation of 1.5 inches. In contrast, the accumulated precipitation at this point last year was quite lower (just 0.6 inches).
Forecast. Weather next week is to be cloudy to partly cloudy with sunny conditions toward the end. A predicted maximum air temperature of about 68° F and minimum temperature of about 35° F are to be expected. Chances of rainfall start off next week and then go away, with little to no rainfall toward week’s end.
GDD or Growing Degree Day by Derek Settle, PhD
It’s that time of year when PGR applications are used to suppress seedheads of annual bluegrass or Poa annua. Some early research was conducted in 2003 by Dr. Randy Kane and Dr. Lee Miller at Aurora Country Club in collaboration with golf course superintendent John Gurke. It was a USGA-funded study and they found a combination of two tank-mixed PGR products could provide Poa seedhead suppression without injury (also known as phytotoxicity). See https://usgatero.msu.edu/tero_browse.html Kane, R., and L. Miller. 2003. Field testing plant growth regulators and wetting agents for seedhead suppression of annual bluegrass. USGA Turfgrass and Environmental Research Online 2(7):1–7.
Years ago, at Michigan State University, Dr. Ron Calhoun developed a temperature-based predictive model called the MSU Proxy/Primo Seedhead Timer. It was one of the original models that became a part of a website that Ron also helped to develop. The audience? Golf course superintendents and other turfgrass growers. Originally, only a limited number of states (Michigan, Wisconsin, Indiana and Illinois) were able to graphically see the predictive pest models. At that time, the Chicago District Golf Association kicked in funding so that Illinois would show up on the map. It was (and remains) simple. The color green indicates the ideal time to initiate pesticide applications. Driven by warming temperatures in the springtime, the bands of color move up the United States (from south to north). Today, there are many more states (and turfgrass managers) that are benefit. For more information see https://gddtracker.msu.edu/.
Poa annua Seedhead Suppression by Shehbaz Singh, MS
Life cycle. Annual bluegrass or Poa (Poa annua) has smooth leaf blades with boat-shaped tips. It is an attractive-looking grass that is bright green and fine textured. However, it lacks heat-tolerance and is highly susceptible to key fungal diseases (anthracnose and summer patch). Poa is a cool-season grass with two types of growth habits. Annual types are typically found in lawns and parkways. Perennial types are common on golf courses. Poa has whitish seedheads and is a prolific producer of seeds. A majority of seedhead production occurs during the spring. Seed clusters (panicles) are 1–4 inches long. Seeds are about 1/16 inch long and amber in color. When seeding, Poa is unattractive and disruptive to golf’s playing surfaces.
Seedhead-suppression. A new way to suppress Poa annua seedhead production is a late fall timing of Proxy (ethephon) plant growth regulator. This can then be followed by one or two applications in spring. In the spring, Proxy PGR is usually combined with Primo Maxx PGR (trinexapac-ethyl) to help reduce risk of phytotoxicity. Avoid using Primo in the first spring application as it can extend the dormancy time or delay the spring green-up of creeping bentgrass. For effective control, mowing should be delayed for at least 2 hours after application. Proxy absorption primarily occurs through the flag leaf and not the lower leaves. Recent research suggests that delaying mowing after application will help ensure PGR absorption and transportation; this results in better seedhead suppression.
Application Timings
• Fall Application: Proxy PGR application should be done immediately after last mowing.
• First Spring Application: In the northern U.S., Proxy PGR application should be done:
Before or at Poa annua boot stage
Growing degree days (base 32 ° F) equals to 200–500. [www.gddtracker.net]
First sign of bloom in forsythia shrub.
• Second Spring Application: Tank-mixture of Proxy PGR + Primo Maxx PGR applied 21–25 days after initial application.
For more on this topic please see the fact sheet below by Shehbaz Singh.
